Changing tyre size

[Martin H]

I'm thinking of having two sets of wheels/tyres for dry and wet running respectively, running 185/70/13 in the dry, and 185/60/13 in the wet, on a Vx 8v live axle car. (Reason being that my tyres of choice don't appear to be available in the same size). The car is set up for the 185/70s.

 

My thoughts on the effect of running the smaller tyre are:

 

Lowered centre of gravity & roll centre (might be a good thing)

 

Less ground clearance (bad when getting car on and off trailer)

 

Speedo gives wrong figure (don't care too much since it will be on track)

 

Will do something weird with the power application as wheels will have a smaller circumference with the same diff ratio (will need to rev the engine more, with corresponding drivetrain impact - but probably some other effects as well???)

 

Can anyone enlighten me (from personal experience perhaps) as to how much difference this is likely to make, and whether it's something that I should avoid? This is only for trackdays, so I'm not too concerned if the only noticeable effect is to increase lap times (providing it's only a little 😬).

 

Many thanks

[eric]

My point of view is that there is theory and reality

 

If you go on the G. polley website you will see that

 

185/60 13 are not same dimensions on 032 and 021

032 are lower and 021 lower than average dimension of other road tyre.

 

The 021 in 185/70 13 are actually lower than others.

 

So the best thing to do is to try (not difficult because the life of such tyre are 2/3 year)

Or the best is to find a friend who can loan you a set of wheels + tyre.

 

 

From my side, I have A539 195/50 15 perfect for me(wet and dry)

before I had 195/45 15 (too low )

and I have also 13" with 185/60 13 unused but I must I must be out of my car to go out from my garage.

(on the road, what I prefer in by now 195/50 15..., but 032 have only 20 miles so...)

 

Next set will be 185/70 13" in 021 to see (very good allround tyre)

may be on a new set of minator

 

So I can keep 032 only for the track (which seems to be the right tyre for)

 

So if you don't want to have some stock in tyre, I will go for

185/70 in 13" (021)

or 195/50 15 A539 for lower running cost

 

If it can help

 

Eric