Wider rear tires on a FWD car...
05-25-2010, 05:17 AM
#76
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Re: Wider rear tires on a FWD car...
Agreed.
In any case I beleive the principle at work here is less weight transfer - in either case, causing a reduction in roll resistance for either axle. I think you correct when you wrote that a wider rear track will contribute to less load transfer...but the resistancne to roll us what increases oversteer - a very relative term here. Could simply mean less understeer.
EDIT: To be clear, a swaybar contributes to more or less TLLTD depending upon size and adjustment. A wider track does not, it in fact decreases it. But the increase in roll resistance over either the front or rear axle is what determines balance. So these two tuning tools are different...although they share some obvious outcomes they should be used for tuning in different ways. Track width considerations are much more fundamental that swaybar considerations. A swaybar is a fine tuning tool - or it should be. Track width considerations should be made first as these will affect springs rates, damping rates and swaybar rates.
This may be helpful if we visualize a car as a cube with say Mac Struts at all four corners; equal weight distribution etc...making the front track wider decreases front roll because roll resistance has increased. The same is true for the rear except we get more oversteer. Adding a swaybar contributes to load transfer...a wider track does not. The degree to which we can expect any adjustement to work depends upon actual weight distribution...and perhaps some consideration for which wheels are driven since these provide forward motion.
The cube analogy is not mine...it was characterized by a dutch suspension engineer a while back...called the Zero Car. Reducing CGz is reducing roll moment and = less wieght transfer
In any case I beleive the principle at work here is less weight transfer - in either case, causing a reduction in roll resistance for either axle. I think you correct when you wrote that a wider rear track will contribute to less load transfer...but the resistancne to roll us what increases oversteer - a very relative term here. Could simply mean less understeer.
EDIT: To be clear, a swaybar contributes to more or less TLLTD depending upon size and adjustment. A wider track does not, it in fact decreases it. But the increase in roll resistance over either the front or rear axle is what determines balance. So these two tuning tools are different...although they share some obvious outcomes they should be used for tuning in different ways. Track width considerations are much more fundamental that swaybar considerations. A swaybar is a fine tuning tool - or it should be. Track width considerations should be made first as these will affect springs rates, damping rates and swaybar rates.
This may be helpful if we visualize a car as a cube with say Mac Struts at all four corners; equal weight distribution etc...making the front track wider decreases front roll because roll resistance has increased. The same is true for the rear except we get more oversteer. Adding a swaybar contributes to load transfer...a wider track does not. The degree to which we can expect any adjustement to work depends upon actual weight distribution...and perhaps some consideration for which wheels are driven since these provide forward motion.
The cube analogy is not mine...it was characterized by a dutch suspension engineer a while back...called the Zero Car. Reducing CGz is reducing roll moment and = less wieght transfer
Last edited by meb58; 05-26-2010 at 06:15 AM.
05-26-2010, 12:30 PM
#77
Honda-Tech Member
Re: Wider rear tires on a FWD car...
Thank u again for your comments.
IMHO, when it comes to things like roll resistance, track, etc vs traction or balance or load transfer, it is more important to understand the basics of what is going on, instead of going by "rules" like if you increase track/roll resistance/etc, then this and that will happen.
For example, front end grip is determined by how even the weight distribution between the two tires are. Maybe adding spacers makes it better and maybe it makes it worse, as I showed in my previous example.
Without busting out too much math, the way I think about what happens when you make a change at any end of the car is to first see what it does to the OTHER end, and then see it's effects on the original end.
The cube car is a good example of the intermediate case I mentioned, when adding track doesn't help much, in the way that you think. I thought about it a little last night, and realized that roll resistance is proportional to track^2. (Then I checked the internet to make sure). If u increase the front track by 10%, then the front roll resistance goes up by 21%. Then the total roll resistance goes up by half of that, 10.5%. That means that the car leans by 1/1.105 =.905 as much as before. Because of this, the rear weights get more even, so the rear grip goes up. The front weight distribution is related to track x roll angle, so .905 x 1.1=.995. The front weight distribution stayed the same, and so you did nothing at all for the front grip. So now you have an understeering car even though you increased the front track. (unless I messed up the math somewhere or left out something important)
Next up, if you have a car with a much higher rear roll stiffness than the front (like some people like to set up here), then the rear will limit the roll angle and not the front. So in this case, adding front spacers isn't going to limit the roll as much, but you still have the track x roll angle equation, so the front weights will get more uneven. It seems that adding front spacers on this car will make the understeer worse.
If you have a car with much higher front roll stiffness, then [explanation omitted] adding front spacers can improve the front weight distribution and therefore grip.
Anyway, I just came up with this right now. Maybe it's right and maybe it's not, oh well. For more authoritative information, read a book or ask an expert. In my previous post I wrote "front much heaver than rear" and vice verse, whereas I probably should have said roll stiffness instead.
IMHO, when it comes to things like roll resistance, track, etc vs traction or balance or load transfer, it is more important to understand the basics of what is going on, instead of going by "rules" like if you increase track/roll resistance/etc, then this and that will happen.
For example, front end grip is determined by how even the weight distribution between the two tires are. Maybe adding spacers makes it better and maybe it makes it worse, as I showed in my previous example.
Without busting out too much math, the way I think about what happens when you make a change at any end of the car is to first see what it does to the OTHER end, and then see it's effects on the original end.
The cube car is a good example of the intermediate case I mentioned, when adding track doesn't help much, in the way that you think. I thought about it a little last night, and realized that roll resistance is proportional to track^2. (Then I checked the internet to make sure). If u increase the front track by 10%, then the front roll resistance goes up by 21%. Then the total roll resistance goes up by half of that, 10.5%. That means that the car leans by 1/1.105 =.905 as much as before. Because of this, the rear weights get more even, so the rear grip goes up. The front weight distribution is related to track x roll angle, so .905 x 1.1=.995. The front weight distribution stayed the same, and so you did nothing at all for the front grip. So now you have an understeering car even though you increased the front track. (unless I messed up the math somewhere or left out something important)
Next up, if you have a car with a much higher rear roll stiffness than the front (like some people like to set up here), then the rear will limit the roll angle and not the front. So in this case, adding front spacers isn't going to limit the roll as much, but you still have the track x roll angle equation, so the front weights will get more uneven. It seems that adding front spacers on this car will make the understeer worse.
If you have a car with much higher front roll stiffness, then [explanation omitted] adding front spacers can improve the front weight distribution and therefore grip.
Anyway, I just came up with this right now. Maybe it's right and maybe it's not, oh well. For more authoritative information, read a book or ask an expert. In my previous post I wrote "front much heaver than rear" and vice verse, whereas I probably should have said roll stiffness instead.
Last edited by beanbag; 05-26-2010 at 12:51 PM.
05-27-2010, 05:23 AM
#78
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Re: Wider rear tires on a FWD car...
I read this very quickly...and most of it makes perfect sense. One of your comments is very true...make a change and see what happens. If we make track as wide as possible front and rear - within some set of rules be they common sense or literal racing rules - redcue sprung weight and work around those two fundamental changes we are sure to end up with a pretty fast car...with some work of course.
Re a wider front track on my JCW mini as an example...
The only part that I cannot explain is that I definately notice an pronounced increase in initial turn-in understeer. Steday state grip improves noticably and blance is perfectly rewarding through mid corner and exit. I can work around the initial understeer but it cause a momentary vagueness in the steering that robs a little confidence. I am trying to work around dialing in more rear swaybar...I may have mis-calculated the rear multi-link motion ratio...who knows. This car's only real vise is very poor threshold braking stbility, a common complaint. My old 99si could be trail braked without any drama...if that's the prefered technique. Shockingly different in that repect.
EDIT: I did just learn that the axle with a wider track "...will take a larger portion of weight distribution even though total weight transfer is less."
Re a wider front track on my JCW mini as an example...
The only part that I cannot explain is that I definately notice an pronounced increase in initial turn-in understeer. Steday state grip improves noticably and blance is perfectly rewarding through mid corner and exit. I can work around the initial understeer but it cause a momentary vagueness in the steering that robs a little confidence. I am trying to work around dialing in more rear swaybar...I may have mis-calculated the rear multi-link motion ratio...who knows. This car's only real vise is very poor threshold braking stbility, a common complaint. My old 99si could be trail braked without any drama...if that's the prefered technique. Shockingly different in that repect.
EDIT: I did just learn that the axle with a wider track "...will take a larger portion of weight distribution even though total weight transfer is less."
Thank u again for your comments.
IMHO, when it comes to things like roll resistance, track, etc vs traction or balance or load transfer, it is more important to understand the basics of what is going on, instead of going by "rules" like if you increase track/roll resistance/etc, then this and that will happen.
For example, front end grip is determined by how even the weight distribution between the two tires are. Maybe adding spacers makes it better and maybe it makes it worse, as I showed in my previous example.
Without busting out too much math, the way I think about what happens when you make a change at any end of the car is to first see what it does to the OTHER end, and then see it's effects on the original end.
The cube car is a good example of the intermediate case I mentioned, when adding track doesn't help much, in the way that you think. I thought about it a little last night, and realized that roll resistance is proportional to track^2. (Then I checked the internet to make sure). If u increase the front track by 10%, then the front roll resistance goes up by 21%. Then the total roll resistance goes up by half of that, 10.5%. That means that the car leans by 1/1.105 =.905 as much as before. Because of this, the rear weights get more even, so the rear grip goes up. The front weight distribution is related to track x roll angle, so .905 x 1.1=.995. The front weight distribution stayed the same, and so you did nothing at all for the front grip. So now you have an understeering car even though you increased the front track. (unless I messed up the math somewhere or left out something important)
Next up, if you have a car with a much higher rear roll stiffness than the front (like some people like to set up here), then the rear will limit the roll angle and not the front. So in this case, adding front spacers isn't going to limit the roll as much, but you still have the track x roll angle equation, so the front weights will get more uneven. It seems that adding front spacers on this car will make the understeer worse.
If you have a car with much higher front roll stiffness, then [explanation omitted] adding front spacers can improve the front weight distribution and therefore grip.
Anyway, I just came up with this right now. Maybe it's right and maybe it's not, oh well. For more authoritative information, read a book or ask an expert. In my previous post I wrote "front much heaver than rear" and vice verse, whereas I probably should have said roll stiffness instead.
IMHO, when it comes to things like roll resistance, track, etc vs traction or balance or load transfer, it is more important to understand the basics of what is going on, instead of going by "rules" like if you increase track/roll resistance/etc, then this and that will happen.
For example, front end grip is determined by how even the weight distribution between the two tires are. Maybe adding spacers makes it better and maybe it makes it worse, as I showed in my previous example.
Without busting out too much math, the way I think about what happens when you make a change at any end of the car is to first see what it does to the OTHER end, and then see it's effects on the original end.
The cube car is a good example of the intermediate case I mentioned, when adding track doesn't help much, in the way that you think. I thought about it a little last night, and realized that roll resistance is proportional to track^2. (Then I checked the internet to make sure). If u increase the front track by 10%, then the front roll resistance goes up by 21%. Then the total roll resistance goes up by half of that, 10.5%. That means that the car leans by 1/1.105 =.905 as much as before. Because of this, the rear weights get more even, so the rear grip goes up. The front weight distribution is related to track x roll angle, so .905 x 1.1=.995. The front weight distribution stayed the same, and so you did nothing at all for the front grip. So now you have an understeering car even though you increased the front track. (unless I messed up the math somewhere or left out something important)
Next up, if you have a car with a much higher rear roll stiffness than the front (like some people like to set up here), then the rear will limit the roll angle and not the front. So in this case, adding front spacers isn't going to limit the roll as much, but you still have the track x roll angle equation, so the front weights will get more uneven. It seems that adding front spacers on this car will make the understeer worse.
If you have a car with much higher front roll stiffness, then [explanation omitted] adding front spacers can improve the front weight distribution and therefore grip.
Anyway, I just came up with this right now. Maybe it's right and maybe it's not, oh well. For more authoritative information, read a book or ask an expert. In my previous post I wrote "front much heaver than rear" and vice verse, whereas I probably should have said roll stiffness instead.
Last edited by meb58; 05-27-2010 at 10:02 AM.
05-27-2010, 03:28 PM
#79
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Re: Wider rear tires on a FWD car...
I dunno, maybe it is related to steering geometry or damping. For example, if you reduce mid and low speed front compression damping, the front of the car dips down faster upon initial turn-in, which creates more of a sensation that the front wheels are "digging in". Reducing the compression damping also slows down the initial weight transfer. I think the circle track guys know a lot about this kind of stuff.
06-01-2010, 05:24 AM
#80
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Re: Wider rear tires on a FWD car...
I poured over Milliken this past weekend but there is nothing in particular about Tw changes.
I did recieve a quick note from the engineer I refered to earlier.
Increasing track width over either axle reduces total car weight transfer. Increasing front Tw will reduce rear weight transfer...front weight transfer remains the same but we get an increase in front roll resistance from a larger front Tw. He also wrote that static weight distribution does not matter. He is sending me a calculator...I will pass it along.
To me this reads as more understeer...but I asked him to verify my results. When I experiemented with track width changes I changed nothing else...I am not sure how different weight transfer balances affected my dampers...
I did recieve a quick note from the engineer I refered to earlier.
Increasing track width over either axle reduces total car weight transfer. Increasing front Tw will reduce rear weight transfer...front weight transfer remains the same but we get an increase in front roll resistance from a larger front Tw. He also wrote that static weight distribution does not matter. He is sending me a calculator...I will pass it along.
To me this reads as more understeer...but I asked him to verify my results. When I experiemented with track width changes I changed nothing else...I am not sure how different weight transfer balances affected my dampers...
Last edited by meb58; 06-01-2010 at 12:22 PM.
06-02-2010, 08:33 PM
#81
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Re: Wider rear tires on a FWD car...
speaking of tires.
just received my 205 50 16 star specs.
im currently on 215 45 16 azenis
i lost approximately .75 inch of contact patch. Will the difference in size outweigh the difference in engineering?
just received my 205 50 16 star specs.
im currently on 215 45 16 azenis
i lost approximately .75 inch of contact patch. Will the difference in size outweigh the difference in engineering?
06-03-2010, 04:59 AM
#82
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Re: Wider rear tires on a FWD car...
Typically the size of the contact patch does not change, but its shape does. A wider tire promotes a wider side to side contact patch and thinner fore and after. A more narrow tire promotes a more narrow contact patch side to side and a longer patch fore and aft. The leverage from the wider contact patch is where the increase in grip comes from...and perhaps stickier rubber which equals better mechanical keying.
A wider contact patch can perform more work in much the same way a wider track width can.
A wider contact patch can perform more work in much the same way a wider track width can.
06-03-2010, 06:12 PM
#83
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06-09-2010, 07:15 AM
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Re: Wider rear tires on a FWD car...
http://www.eviltwinmotorsports.com/w...ter-2008.7.pdf
I didn't reread the whole thread, but I don't think was posted. If not, enjoy!
I didn't reread the whole thread, but I don't think was posted. If not, enjoy!
12-04-2019, 09:32 PM
#87
Honda-Tech Member
Re: Wider rear tires on a FWD car...
Nice 9.5 year grave digger session.
FWD drag cars normally run a fatty/skinny setup. High power street FWD setups will also run a wider front tire but for most street applications a matching front and rear tire sizes is just fine.
FWD drag cars normally run a fatty/skinny setup. High power street FWD setups will also run a wider front tire but for most street applications a matching front and rear tire sizes is just fine.
12-05-2019, 03:39 AM
#88
Re: Wider rear tires on a FWD car...
12-05-2019, 05:53 AM
#90
Honda-Tech Member
Re: Wider rear tires on a FWD car...
How big you can go in the rear is chassis dependent. The dc, em1, ej will take a slightly wider rear tire than say an EG, EF, CRX with downforce being equivalent between platforms. I think a little birdie whispered something like 245s on the rear on the EG was slower due to a lack of heat/grip in the rear. During the hot months, it might make sense to go that wide but the other 3 seasons it looks like the max width is somewhere in the 225-235 rear. One thing I have found that helps with the 225s is always starting with a full tank of fuel… helps them tack up faster.
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