Check the web.
The front is one of the "older" style sizes. Your rear has a more modern sizing (and probably a higher technology tire
[TABLE="width: 60%"]
[TR]
[TD="width: 100%, colspan: 6"]
Motorcycle Street Tyre Size Conversion Chart[/TD]
[/TR]
[TR]
[TD="width: 45%, bgcolor: #336699, colspan: 3"]
Front Tyres
[/TD]
[TD="width: 55%, bgcolor: #336699, colspan: 3"]
Rear Tyres
[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]
Metric[/TD]
[TD="width: 16%, align: center"]
Alpha[/TD]
[TD="width: 20%, align: center"]
Inch[/TD]
[TD="width: 5%, align: center"]
Metric[/TD]
[TD="width: 5%, align: center"]
Alpha[/TD]
[TD="width: 11%, align: center"]
Inch[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]80/90[/TD]
[TD="width: 16%, align: center"]
MH[/TD]
[TD="width: 20%, align: center"]
2.50/2.75[/TD]
[TD="width: 14%, align: center"]110/90[/TD]
[TD="width: 20%, align: center"]MP85[/TD]
[TD="width: 21%, align: center"]4.50/4.75[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]90/90[/TD]
[TD="width: 16%, align: center"]
MJ90[/TD]
[TD="width: 20%, align: center"]
2.75/3.00[/TD]
[TD="width: 14%, align: center"]120/90[/TD]
[TD="width: 20%, align: center"]MR90[/TD]
[TD="width: 21%, align: center"]4.50/4.75[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]100/90[/TD]
[TD="width: 16%, align: center"]
MM90[/TD]
[TD="width: 20%, align: center"]
3.25/3.50[/TD]
[TD="width: 14%, align: center"]130/80[/TD]
[TD="width: 20%, align: center"] [/TD]
[TD="width: 21%, align: center"]5.00/5.10[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]110/90[/TD]
[TD="width: 16%, align: center"]
MN90[/TD]
[TD="width: 20%, align: center"]
3.75/4.00
[/TD]
[TD="width: 14%, align: center"]130/90[/TD]
[TD="width: 20%, align: center"]MT90[/TD]
[TD="width: 21%, align: center"]5.00/5.10[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]120/80[/TD]
[TD="width: 16%, align: center"] [/TD]
[TD="width: 20%, align: center"]
4.25/4.50[/TD]
[TD="width: 14%, align: center"]140/80[/TD]
[TD="width: 20%, align: center"] [/TD]
[TD="width: 21%, align: center"]5.50/6.00[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]120/90[/TD]
[TD="width: 16%, align: center"]
MR90[/TD]
[TD="width: 20%, align: center"]
4.25/4.50[/TD]
[TD="width: 14%, align: center"]140/90[/TD]
[TD="width: 20%, align: center"]MU90[/TD]
[TD="width: 21%, align: center"]5.50/6.00[/TD]
[/TR]
[TR]
[TD="width: 13%, align: center"]130/90[/TD]
[TD="width: 16%, align: center"]
MT90[/TD]
[TD="width: 20%, align: center"]
5.00/5.10[/TD]
[TD="width: 14%, align: center"]150/80[/TD]
[TD="width: 20%, align: center"]MV85[/TD]
[TD="width: 21%, align: center"]6.00/6.25[/TD]
[/TR]
[TR]
[TD="width: 49%, colspan: 3, align: center"] [/TD]
[TD="width: 14%, align: center"]150/90[/TD]
[TD="width: 20%, align: center"]MV85[/TD]
[TD="width: 21%, align: center"]6.00/6.25
[/TD]
[/TR]
[/TABLE]
Here is a list I googled