If it's a Silent "Spinner" (not Silent Runner) there have been issues with them since a manufacturing change - usually it's that they are too stiff and don't spin well. I believe they do make a 10" version now - someone had issues with the 10" version recently in that it wasn't working properly. Otherwise, as Souffle said, they only make the 6.5" or 12" version. I wouldn't use any of them personally as they have too many issues these days - usually just too stiff to spin! And not that silent really.
Are you in the US? Good wheels for a Syrian are 11" Wodent Wheel, 12" Silent "Runner" (not "Spinner") - both of which can be ordered from Exotic Nutrition online who sell them at a good price, and the 10" Carolina Storm wheel which is ordered direct from their website - but it's quite expensive.
If your tank is tall enough I would recommend the 12" Silent "Runner" - it is 35cm tall on its stand, if that fits. It has a very good, safe, sturdy metal stand and would work well in a tank - it sits a bit higher than the wodent wheel so easier to have enough substrate under it. Ideally the base would sit on the base of the tank and you just have the substrate on top of the base, under the wheel - to make sure it's stable.
You could then just have slightly lower substrate in that area of the cage, sloping to deeper elsewhere. Some people "fence off" the wheel area and have split level substrate that way.
The Carolina Storm wheel has a height adjustable stand - so you can raise its height so there is more substrate under the wheel. It's only 10" diameter but that should be fine for an average syrian. A large syrian may be better with 11" or more.
The 12" Silent "Runner" is bigger than it needs to be but it is quite compact depthwise and very easy for hamsters to run in as it spins really well (some Silent "Spinners" can be quite stiff for running in and not spin well). It's also well made - had mine 2.5 years with no issues. It is properly silent as well as it has bearings.
The Carolina Storm wheel is also silent with bearings and also has a safe sturdy stand. However it is much deeper so can be bulky in a cage, ie using up a fair bit of space, depending on how big your tank is.
So basically it does sound like you need a new wheel. If you haven't had your current one very long, take it back for a refund and say it's faulty (which it sounds like it is) and not big enough. Hopefully you'll get a refund.
I'm linking the wheels mentioned, in case you're in the US! If you're in the Uk there are other choices from Zooplus, but also the Silent Runner is sold by the Sugar Glider shop in the Uk.
https://www.exoticnutrition.com/Prod...r)__43673.aspx
https://www.exoticnutrition.com/Prod...-11__WW11.aspx
Carolina Storm wheel - pick your colour!
https://www.carolinastormhedgehogs.c...orm-wheel.html