BMW M5 Forum and M6 Forums banner

Less understeer - changing tire size on front rims?

2K views 11 replies 7 participants last post by  stever 
#1 ·
Has anyone tried going to a slightly wider tire size on their front rims with the stock wheels? I do not really want to do a dinan suspension kit or anything and I love the stock look of the M5 wheels. So if anyone has tried 255s on the front I would love to hear if it felt appreciably different.
 
#2 ·
brparker,

New summer tyres are coming on within a couple of weeks.
Fronts will be 255/35-18. I am also interested in feedback from anyone who have tried this and unless we get that feedback I'll be able to provide it within a couple of weeks.

Cheers,
/Johan
 
#3 ·
Dinan recommended a similar mod for the M3 by running 245s and 8.5" rims up front vs 225s and 7.5" rims.

I bet that the hot setup, would be running the 9.5s and 275s up front... Will probably need a 10-15mm spacer to make this work.

JL
 
#4 ·
When I get around to it (that'll be after the SHO engine is finished, and after the Mustang electricals/fuel cell/Tremec/Sierra brakes are done, and after the frame is back in the '64 wagon, and after the plans are settled for the house remodel, and if I have $.50 left after all that...) my attempted understeer fix will be:

a) 1mm more rear anti-roll bar
b) Swapping the friction-type limited-slip for a Gerodisc/Viscolok or Quaife.

I've become pretty convinced that the clutch-type limited slip is creating a fair bit of turn-in 'push', even in slow-speed (maybe especially in slow-speed) use.

I'm not willing to go to significantly larger front tires, as that will likely detract considerably from steering feel.


[This message has been edited by JEM (edited 13 March 2001).]
 
#6 ·
You have to do the calculation to ensure that you have the same rolling radius. This started with Porsche and Alpina (which originally used 205/55x16 on the front of 5 and 7 series and 225/50x16 on the rear. In order to avoid some problems and inacuracies in speedometer, you need to ensure the same rolling radii.

Rick
 
#7 ·
Originally posted by raland9:
In order to avoid some problems and inacuracies in speedometer, you need to ensure the same rolling radii.
I can see how a change in rolling radius on rears can affect the speedometer but what has this do do with changing tire size on the fronts?

I am pretty sure that increased grip on fronts would lessen the cars tendency to understeer. When you setup a reace car you start with the rear iand if understeers one common way of reducing this is to add more grip to the front, how can this be wrong?

Hasn't anyone tried this already?

Cheers,
/Johan


[This message has been edited by johann (edited 13 March 2001).]
 
#8 ·
Changing rolling radius significantly could screw up the ABS/DSC.

Still, going from a 245/40 to a 275/35-18 would not change the rolling radius significantly.

As for steering feel, it's been my experience that putting significantly more rubber on the ground tends to drive steering effort up but drive feel down. Some cars are more sensitive to this than others.

I recall driving one E34 M5 that had some big wheel/tire setup (265/35-18 fronts?) and the thing felt like someone had filled the steering box with molten lead. The next E34 I drove was stock with 235/45-17s and it felt a thousand pounds lighter.

OTOH, my track Mustang has 255/40-17s on the front and its steering is almost too light, and has plenty of feedback.
 
#9 ·
Fredcourtot should be able to shed some light on this issue. He's running the 275/35/18's front and 285/30/18's rear. Check with him and see what his response would be on handling feel.
I have the new Dinan wheel set up on order.
Hope to have them by the end of the month.

------------------
Mark
2000 Dinan M5
2001 X5 4.4 Sport

Mark's M5 Page
X5 Page
modo2@email.msn.com
 
#10 ·
I ran some numbers on different wheel sizes than the stock configuration. Does anyone know how much difference would be a problem? Here are the numbers, any advice would be appreciated.

(I can not figure out why there is so much space below)

<table border=0 cellpadding=1 cellspacing=0> <tr> <td colspan="5"> <font face="Arial, Helvetica, sans-serif" size="2" color="#0000FF">Front Wheels</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">   Width</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">   Aspect</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">   Rim</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">   Radius</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">   % difference</font></td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">245</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">40</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.86</font> </td> <td> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">255</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">40</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">13.02</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">1.22%</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">265</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">35</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.65</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">-1.61%</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">275</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">35</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.79</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">-0.54%</font> </td> </tr> <tr> <td> </td> <td> </td> <td> </td> <td> </td> <td> </td> </tr> <tr> <td colspan="5"> <font face="Arial, Helvetica, sans-serif" size="2" color="#0000FF">Rear Wheels</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">Width</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">Aspect</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">Rim</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">Radius</font></td> <td> <font face="Arial, Helvetica, sans-serif" size="2">   % difference</font></td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">275</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">35</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.79</font> </td> <td> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">285</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">35</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.93</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">1.08%</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">295</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">35</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">13.06</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">2.15%</font> </td> </tr> <tr align="right"> <td> <font face="Arial, Helvetica, sans-serif" size="2">295</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">30</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">18</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">12.48</font> </td> <td> <font face="Arial, Helvetica, sans-serif" size="2">-2.39%</font> </td> </tr></table>

[This message has been edited by brparker (edited 13 March 2001).]
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top