wheel/tyre sizes - be careful when replacing

[jphanna]

This is something that may happen to you without being aware. My Taxi pack VE came out with 16 steels and I was going to get rid of them as soon as I found the rims I liked the best. After 6 months I decided the Caprice rims were the best for me. they are 18”. So once I got the size settled I rang around to find suitable tyres. I gave to numerous tyre dealers the exact tyres size of old rims/tyre combo. They all said I had to have 245/45/18. that was the exact match in size.

Well I noticed that when I put em on that the car felt like the hand brake was on, or it was going up hill, it felt less perky in acceleration. Anyway I thought it was extra weight so I thought I will accept it as car looks real classy now and put it out of my mind.

I was fiddling around the garage and I rolled out the old 16 wheel tyre and it’s 25mm smaller than the 18”ones on the car. that is a massive difference so my speedo will be out as well. Next time some tyre expert tells you that you have to have a certain size, take your old rim/tyre there and put it next to the ones they are proposing

[Mr Hardware]

http://www.miata.net/garage/tirecalc.html
always visit here for tyre changes
if your original tyres were 215/60/16 then they should have put 235/45/18s on.

[LowEL2XR8]

I've stated in my other thread here that those tyre change calculators aren't accurate. They reckon there was 4mm difference in diameter from my 17s to 19s when in fact it lifted my car off the deck by at least 20mm.

[4Vman]

Originally Posted by jphanna

This is something that may happen to you without being aware. My Taxi pack VE came out with 16 steels and I was going to get rid of them as soon as I found the rims I liked the best. After 6 months I decided the Caprice rims were the best for me. they are 18”. So once I got the size settled I rang around to find suitable tyres. I gave to numerous tyre dealers the exact tyres size of old rims/tyre combo. They all said I had to have 245/45/18. that was the exact match in size.

Well I noticed that when I put em on that the car felt like the hand brake was on, or it was going up hill, it felt less perky in acceleration. Anyway I thought it was extra weight so I thought I will accept it as car looks real classy now and put it out of my mind.

I was fiddling around the garage and I rolled out the old 16 wheel tyre and it’s 25mm smaller than the 18”ones on the car. that is a massive difference so my speedo will be out as well. Next time some tyre expert tells you that you have to have a certain size, take your old rim/tyre there and put it next to the ones they are proposing

Most factory mag wheels are damn heavy.

[flappist]

Originally Posted by 4Vman

Most factory mag wheels are damn heavy.

Mine aren't

[Elks]

[QUOTE=Mr Hardware
if your original tyres were 215/60/16 then they should have put 235/45/18s on.[/QUOTE]

However Holden fitted 245/45/18's as standard to my Calias V.

[gossy]

Originally Posted by 4Vman

Most factory mag wheels are damn heavy.

And stronger than most cheapa_s aftermarket rims.

[Mr Hardware]

Originally Posted by myts

However Holden fitted 245/45/18's as standard to my Calias V.

Well thats an interesting observation, but my point was more about what the original tyres were. What is the std size for a VE with steelies?

[jphanna]

[QUOTE=myts]

Originally Posted by Mr Hardware
if your original tyres were 215/60/16 then they should have put 235/45/18s on.[/QUOTE

However Holden fitted 245/45/18's as standard to my Calias V.

i have no doubt the guy was doing what he thought was correct, according to HIS guidlelines. i am not having a dig at him....but his guidelines are wrong. I recon Bob Jane TM are great and have no probs with service. I will be back for sure. i was just shocked at size difference and now i know why car felt like handbrake on when i left the driveway.

I will in future ask for the tyre that THEY propose, put it next to the old ones on the car and physically check them for same height.

[Mr Hardware]

WHAT is THE std SIZE for A VE with STEELIES?

[jphanna]

Originally Posted by Mr Hardware

WHAT is THE std SIZE for A VE with STEELIES?

car is home, have to wait till i get home to read it. will send after 6.00pm.

its ok, because they 18's are on now and it looks great. i only checked them yesterday against new rim/tyres, so i been driving for quite a while without knowing size diffrence.

[prydey]

luxury cars run a higher profile tyre than the sports counterparts to keep the ride soft. this will be allowed for in the ecu/pcm.

i put 18" g6et rims on my bf2 wagon and they are about 10mm smaller diameter than 16" stockies. i've since had the tyre size changed in the pcm, however even before i did this the speedo didn't appear to be out much, if at all. i have heard that on the later model cars it gets the reading from the abs sensor or something and doesn't affect speedo. not sure on that though.

[GasoLane]

Originally Posted by jphanna

I gave to numerous tyre dealers the exact tyres size of old rims/tyre combo. They all said I had to have 245/45/18. that was the exact match in size.

SNIP....................

Next time some tyre expert tells you that you have to have a certain size, take your old rim/tyre there and put it next to the ones they are proposing

They were probably correct in that might have been the right size for the RIM. next time tell them what car your fitting them as well.

Oh, and dont forget the insurance side....if the rims/tyres are NOT what was specced for the car, lookout at claims time!

[kramo]

I'm pretty sure the Omega's come with 225/60 R16 which is only about 1mm different to the 245/45 R18. Check what your tyre placard says.

[BlackLS]

Keep in mind tyre wear affecting the height of the tyre. Also the taller profile tyre will flex more therefore reducing the rolling circumference.

[MR.BA.GT.332]

i know this isnt QUITE related to topic's car involved, but my EB has the factory 15in alloys with bridgestone G grid rubber (cant remember size off the top of my head) but when i had my 16in simmons on the car with 245/45/16 tyres, the car was a lot snappier with the 16's but the rolling diameter was smaller, and once i put the 15's back on with taller diameter, made the car feel like a slug... so i understand where your comming from JPHANNA... gotta be careful cause if the car was for all out performance if not careful could hurt the performance instead of enhancing it.

[jphanna]

Originally Posted by Mr Hardware

WHAT is THE std SIZE for A VE with STEELIES?

got figures (i checked my insurance before i changed rim/tyres combo. i was going to get the Bob Jane - LINEAR (sexiest wheel i ever seen) but it wasnt legal on mine as only 19" could fit. Insurance said 18" was limit.


16" - 225/60/16

18" - 245/45/18.

for my car, which has standard suspension and has huge amount of room under guards....its not an issue, but for you guys with your lowered cars, im sure if you had to deal with 25mm that you didnt count on, it could be an issue. the tyre guys are doing there stuff by the book and i dont blame them one bit.

IF YOU HAVE LIMITED SPACE UNDER GUARDS...it may be handy to check yourself rather than take their advice according to their references.

[jphanna]

Originally Posted by mr_460bigblock

i know this isnt QUITE related to topic's car involved, but my EB has the factory 15in alloys with bridgestone G grid rubber (cant remember size off the top of my head) but when i had my 16in simmons on the car with 245/45/16 tyres, the car was a lot snappier with the 16's but the rolling diameter was smaller, and once i put the 15's back on with taller diameter, made the car feel like a slug... so i understand where your comming from JPHANNA... gotta be careful cause if the car was for all out performance if not careful could hurt the performance instead of enhancing it.

i have a taxi pack VE, performance is not a priority for a car like this. The car in your avatar, thats a diffrent story...

[Yellow_Festiva]

Originally Posted by LowEL2XR8

I've stated in my other thread here that those tyre change calculators aren't accurate. They reckon there was 4mm difference in diameter from my 17s to 19s when in fact it lifted my car off the deck by at least 20mm.

Tyre change calculators are never wrong. They are based on a simple mathematical equation.

What is 'wrong' in reality is the discrepancies between tyre manufacturers for a certain size. Having said that, I would bet that X size tyre across several different manufacturers may only have a 1-3mm variation across the board, in terms of overall diameter when fitted to identical rims.

Your 17->19 example is greatly flawed (by either your measurements or the info you entered into the calculator) if the calculator said that 4mm of difference in diameter was really 40mm in reality (seeing as if a car is jacked up 20mm, this represents half the total diameter).

Jason

[smacxr8]

Originally Posted by jphanna

got figures (i checked my insurance before i changed rim/tyres combo. i was going to get the Bob Jane - LINEAR (sexiest wheel i ever seen) but it wasnt legal on mine as only 19" could fit. Insurance said 18" was limit.


16" - 225/60/16

18" - 245/45/18.

for my car, which has standard suspension and has huge amount of room under guards....its not an issue, but for you guys with your lowered cars, im sure if you had to deal with 25mm that you didnt count on, it could be an issue. the tyre guys are doing there stuff by the book and i dont blame them one bit.

IF YOU HAVE LIMITED SPACE UNDER GUARDS...it may be handy to check yourself rather than take their advice according to their references.

The 245/45 18's should have been the right tyre then.

Calculation-
225 x 60% x2 + (16 x 25.4) = Rolling diameter 676mm
245 x 45% x2 + (18 x 25.4) = Rolling diameter 677.5mm
Thats only 1.5mm difference in diameter, which should have been the closest you are gonna get.

[LowEL2XR8]

Originally Posted by Yellow_Festiva

Tyre change calculators are never wrong. They are based on a simple mathematical equation.

What is 'wrong' in reality is the discrepancies between tyre manufacturers for a certain size. Having said that, I would bet that X size tyre across several different manufacturers may only have a 1-3mm variation across the board, in terms of overall diameter when fitted to identical rims.

Your 17->19 example is greatly flawed (by either your measurements or the info you entered into the calculator) if the calculator said that 4mm of difference in diameter was really 40mm in reality (seeing as if a car is jacked up 20mm, this represents half the total diameter).

Jason

I know its really wierd. They guy that bought my 17s measured them up against his 19s and they were equal. I can't work out why there is such a difference but there is.
It can't be tyre wall flex cause 17"s wouldn't flex 20mm with the weight of the car on them would they?

All I can assure you is that my car is at least 20mm higher off the gound going from 17"s to 19"s

[Yellow_Festiva]

Originally Posted by LowEL2XR8

I know its really wierd. They guy that bought my 17s measured them up against his 19s and they were equal. I can't work out why there is such a difference but there is.
It can't be tyre wall flex cause 17"s wouldn't flex 20mm with the weight of the car on them would they?

All I can assure you is that my car is at least 20mm higher off the gound going from 17"s to 19"s

Hmmm interesting if they were matched and found to be equal.

Can you post the sizes the of the 17 and 19inch size combo fitted?

[LowEL2XR8]

Yep no worries Yellow Festiva; my 17" tyres size were 235/45R17 and the 19"s are 235/35R19.

[xbgs351]

Originally Posted by jphanna

Well I noticed that when I put em on that the car felt like the hand brake was on, or it was going up hill, it felt less perky in acceleration. Anyway I thought it was extra weight so I thought I will accept it as car looks real classy now and put it out of my mind.

I was fiddling around the garage and I rolled out the old 16 wheel tyre and it’s 25mm smaller than the 18”ones on the car. that is a massive difference so my speedo will be out as well. Next time some tyre expert tells you that you have to have a certain size, take your old rim/tyre there and put it next to the ones they are proposing

The larger tyre diameter is equivalent to running a taller differential, which will reduce the acceleration. Also the heavier weight of the larger wheels will mean that they have a greater moment of inertia, which is equivalent to running a heavier flywheel. This will also reduce the cars acceleration and make it less perky.

[Yellow_Festiva]

Originally Posted by LowEL2XR8

Yep no worries Yellow Festiva; my 17" tyres size were 235/45R17 and the 19"s are 235/35R19.

According to my pen and paper working out. The 17 inch combo should have a total diameter of 643.3mm (call it 64.3cm) and the 19inch combo will have a total diameter of 647.1mm (call it 64.7cm).

So around 5mm difference. Hmmm wonder what else could cause the hike in ride height?

[LowEL2XR8]

Its got me baffled as well.