Selecting Car (Toyota) Tyres - Different Sizes

s0805 on 21/07/2016 - 09:12
Last edited 22/07/2016 - 18:25 by 1 other user

Hi there,

Need some assistance on selecting tyre size for my toyota 2000. currently it has 185/75 R14 89H. Can I replace them with
(185/65 R14 86H) OR (185/70 R14 88H). If both can be used for replacement is one better than the other?

Also, what are the implications if any where my spare tyre is different size (i.e. 185/75 R14 89H) and rest of them are any of the above two. does that cause issue when i change/use my spare tyre…

am i best in assuming the closet to my existing tyres is better. I mean select 185/70 R14 88H cause currently I've 185/75 R14 89H.

cheers

Automotive

Comments

SnoozeAndLose on 21/07/2016 - 09:17

By Selecting with size Tyre (185/65 R14 86H) OR (185/70 R14 88H), they will affect the diameter of the tyre which may affect the odometer as well as the speedo may not be accurate due to reduced Tyre diameter.
- s0805 on 21/07/2016 - 09:24
  
  so does that mean i should stick to my existing tyres 185/75 R14 89H. Given that's what my car is used to?
  
  Keep in mind if I change I'll change all four together same size but yes the spare will be original old size.
  - SnoozeAndLose on 21/07/2016 - 09:26
    
    I think so, if you want to change you should change the whole set rim = tyres.
    - s0805 on 21/07/2016 - 09:39
      
      ok. I thought R14 was the key that i can't change unless i fit in new rims..
    - SnoozeAndLose on 21/07/2016 - 10:40
      
      @s0805:
      
      Yuu can change a different size Tyre, just the wall thickness will be reduce so as to not affecting the overall diameter.
Nugs on 21/07/2016 - 09:26

You will be using tyres which do not have the same load carrying capability (the 88 vs 89), higher number equals more load carrying capacity.
You 'might' have insurance issues in the event of a claim as vehicle would no longer be technically legal assuming the 185/75 is standard size. You should refer to tyre placard which is a sticker normally found in glove box or door jam.
car will also be 5-10mm closer to ground (if that matters to you).
- s0805 on 21/07/2016 - 09:41
  
  i've looked that sticker you mentioned it says recommended size is 185/75. However for load it mentions minimum is 86H which covers both (185/65 R14 86H) OR (185/70 R14 88H). I am keeping 185 part the same as wekll, it's just the 75 part will be changed.
altomic on 21/07/2016 - 09:36

185 is the width of the tyre in millimetres.
60 is the aspect ratio or tyre profile i.e height- of the actual tyre from rim to edge
R means it is radial construction.
15 is the diameter of the wheel rim in inches.

the main difference is the aspect of the tyre . - the second number 75 or 65 or 70.

the smaller the second number then the slower the car will drive (more rotations of the tyre)

it's best to keep the same tyre size (second number) as your cars speedo is set for that size.

if a car with 75 size tyres is travelling at 32.19 km/h then a car with 65 size tyres will be doing 30.31 km/h at the same RPM

so if you get new tyres with a larger aspect e.g. 80, then your car will actually be moving faster than your speedo tells you. =speeding ticket if not careful.

here is a useful site to explain tyre numbers

if you have a spare with a different size (second number) then using it for shortish trips is fine. The car may feel a bit wobbly. I had an odd tyre on a previous car (got a blow out in the middle of no-where and local garage only had an odd tyre). The car drove fine. I got used to it. but new passengers would comment.

the last digit/code is 2 pieces of information - the load/speed index
the numbers explain the tyres load capacity
the letter explains the speed rating of the tyre

here is a better explanation/summary

so, basically get the same size tyre - the size/rating, etc is the best match for your car/odometer.

a set of 185/70 R14 88H tyres will be fine. you'll just be travelling a few Km/h slower than with 75's
- s0805 on 21/07/2016 - 09:46
  
  Thanks for that. Very helpful. So if i change the second number 75 closest to what i currently have will be better (i.e. 70 is better than 65). If i change 75 to 70 my car odmoneter and speedo will not be pinpoint accurate. Can that be corrected or is it hard coded.
  
  Also, good to know from your experience that different size of spare tyre can be ok in emergencies…
  - altomic on 21/07/2016 - 10:03
    
    it would be hardcoded.
    
    the smaller that number / the slower you go (at the same RPMs).
    
    but also the smaller the tyre then the less tyre surface you have on the road. i.e. less grip area.
    
    for a 70 vs 75 this would be very marginal.
    
    also the tyre PSI (air in the tyre) would impact as well. if the 70 had a lower PSI/less air then it would be "squishier" and have a larger grip area compared to if it was its correct PSI.
    
    a lot of cars have those tiny spare tires. they recommend not to go over a certain speed limit with them. and to only use them for a short distance. etc.
s0805 on 21/07/2016 - 10:37

excellent. I'll check both 70 & 75 quotes. At least this gives me the option and with number of offers going on may find some deals around it. cheers
spackbace on 21/07/2016 - 10:47

http://www.tyresizecalculator.com/tyre-wheel-calculators/spe…

185/65 R14 86H - Speedometer reads 100, but the actual speed is 94 km/h
185/70 R14 88H - Speedometer reads 100, but the actual speed is 97 km/h

So i'd stay away from the 65s, too different to your factory tyre
- battler on 21/07/2016 - 12:01
  
  agree with the way the calculator works, but bit misleading that they use the term 'actual speed', as it does not allow for any discrepancy between speedo speed (with factory fitted tyres) and real actual speed (not sure what the appropriate term is here - perhaps 'land speed')
  - spackbace on 21/07/2016 - 12:05
    
    But that's a different problem again, and 1 that will only better/worsen the speed difference.
    
    IE speedo might say 100kph now, GPS speed is really 95kph, '65' tyre will worsen it by a further 6%, so fitting that tyre will give a GPS speed of 89.3kph, but speedo says 100kph…
    
    With a discrepancy like that, either:
    a) you'd constantly hold traffic up, and wonder what was going on (if you drive with the needle dead on 100kph), or
    b) you wouldn't have to worry about speeding fines if you thought you were driving 10kph over the limit (if you drive @ 110kph).
    - battler on 21/07/2016 - 12:53
      
      maybe that's the problem with all the right hand lane hogs on the freeway!!
      ;)
    - spackbace on 21/07/2016 - 13:13
      
      +1
      
      @battler:
      
      Don't get me started! :P
- s0805 on 21/07/2016 - 12:59
  
  Agreed. 75 is 1st preference followed by. the lower the number compare to what I've, will be more discrepancies.
paulieau on 22/07/2016 - 08:35

I just went through this with my partners car, I saw a set of 4 which was $60 a tyre cheaper but the aspect ratio was different by 5, rang up the tyre place and asked the implications of changing away from the manufacturer recommendations and he flat out told me they wouldn't do it because it would throw the speedometer out and also make the car unroadworthy (I'm in Vic). So I'd suggest you might have trouble finding a tyre place to fit them outside the recommendations.
- s0805 on 22/07/2016 - 09:50
  
  can you share what tyre company that was. I'm in VIC as well. I find interesting that car can become unroadworthy feedback at the end of the day sticker in car says this is RECOMMENDED size. I agree that putting slightly different than recommended size will throw speedo out by something but does it make it unroadworthy (its' far stretch).
  
  I've not talked to any of them yet but I guess if they not willing to do it then i can't do much about it. On the other hand do Wheel alignment comes standard with replacing tyres or is it extra?
  - paulieau on 23/07/2016 - 18:20
    
    It was beaurepaires that refused to do it stating it would be unroadworthy. They explained because of the speedo being thrown out. Likewise I find it strange, but didn't argue the point. Wheel alignment is generally extra at about $70-80
    - s0805 on 24/07/2016 - 10:45
      
      Thanks
Euphemistic on 22/07/2016 - 09:20

And just to throw another spanner in the works you could also get a wider tyre with a lower profile, or a narrower tyre with a higher profile to keep the rolling diameter the same.

eg a 215/65R14 or 165/85R4 tyres will have very similar rolling diameter to 185/75R14. According to the calculator above will only read 1km/h different if over 120km/h.

First three numbers are the width in mm 185mm wide, the next two numbers are the profile, the height of the tyre as a percentage of the width. so a 185/75 tyre is 185mm wide and 139mm high from the rim. 215/65 tyre is 215mm wide, 140mm high and 165/85 is 165mm wide and 140mm high, hence the total diameter being the same and not affecting your speedo reading.

Using a different sized tyre as a spare will work. It may feel a bit different, but a close match should not be noticable. If you are using a different sized spare it is better to have it on the non-driving wheels (back on a front wheel drive car). The different sized spare is also the reason a lot of spare tyres advise you not to exceed 60/80km/h with them fitted.
- s0805 on 22/07/2016 - 09:52
  
  Thanks for that. Spare tyre will be used only for emergencies. Tyre size I've is not that common hence investigating this option.
Gershom on 22/07/2016 - 11:23

Why? Why not go with the regular tyres? Are the other ones cheaper? If so, how much cheaper? Why on earth would anyone bother?

Selecting Car (Toyota) Tyres - Different Sizes

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