Changing from 195 to 205 tyres on 15 inch wheels?

Nelson_Wilbury · Post by **Nelson_Wilbury** » Sun Jan 26, 2003 10:40 pm

I imagine it'll look nicer but any grip gains as i've heard the wider the tyres get the less the grip?

polo2k · Post by **polo2k** » Mon Jan 27, 2003 11:04 am

personally id say no because 55hp wont really get them o optimum temp so if you go wider then the tyre stays colder and thus grips less due to not being able to change to the contours of the road. the only reason why that would be a good idea is if the 195`s are getting hotter
dont forget a 205/50/15 has a taller sidewall than a 195/50/15
but if thats the look you like then go for it cos its your car and its you who has to drive it

Nelson_Wilbury · Post by **Nelson_Wilbury** » Wed Mar 19, 2003 7:13 pm

Coming back to this topic...

When I get my 16 inch wheels I wanna get wider 205 tyres instead of 195. I was also gonna get a lower 40 profile (instead of 45). Would the wider tyre balance out the slighty lower profile as I've heard most people say making the tyres wider will bugger up the speedo (not sure if theres any truth in that though

Speedlaw · Post by **Speedlaw** » Wed Mar 19, 2003 7:45 pm

The number of revolutions your tyres make influence the speedo, so if you get wider tyres with the same percentage of tyre-wall height the speedo will be underrating your speed.

So, as a rule of thumb, wider tyres means lower sidewalls. Same with bigger rims, they require lower tyre walls to compensate for the bigger wheel diameter.

polo2k · Post by **polo2k** » Wed Mar 19, 2003 8:47 pm

the way it works is that the side wall height is relative to the middle number i the tyre size so if you have 195/50/15 tyres then the tread is 195mm wide and the sidewall is 50% of that so if you go to 205 from 195 and go from 50 -45 then the diference is minimal

the spedo issue is all about the total rolling diameter of the tyre so if you go from 165 65 13`s to 15" wheels then assuming you are going to run a 195 wide (common size) then you need to drop to around 45-50 (it falls inbetween in this case) to keep the total type diameter tehe same because for every inch you add to the total dimater of a tyre then the circumfrence will be upped by aroung 1 foot which when multiplied by the number of revolutions that a tyre can make per mile can ammount to quite a large difference
the rule is that if the over all diameter is LARGER then the spedo will be slightly "slow" (acceleration will also suffer slightly)
however if its smaller then the reading will be higher th=an the truth and acceleration will benefit slightly
as a sidenote some people use a lower profile to gain acceleration and also when they go on a rolling road as you can get slightly higher power readings